The automobile engineering thread

Sitting at a stoplight next to a Model S recently, I noticed that the rear brake discs have two sets of calipers on them: one large one at the rear (looking at the right side, at ~9 o'clock), and another smaller one, about 1/3 the size, at about 1 o'clock. What's all that for? Is it a parking brake, or for some other auxiliary purpose?

Almost certainly the handbrake/parking brake. Usually the singular rear calipers have a fitting for a mechanical cable, but occasionally a separate caliper is fitted for some reason.

I'm in agreement with Raptor on the ABS issue. What I don't understand is why it seems so difficult for manufacturers to fix the problems with ABS, because an automated solution that works correctly should be able to perform as well as a superbly trained driver and be consistent. I think most drivers are woefully undereducated as to how vehicles work, and the difference in stopping distance on ultra low friction surfaces between cadence braking and ABS is quite an eye opener.

It's not just an academic issue either ; on hills covered in ice I've watched a whole line of cars just hard on the brakes, wheels locked and sliding inexorably into the pile of crashed vehicles at the bottom. Meanwhile, with cadence braking correctly applied, you can maintain a degree of control over vehicle direction whilst slowing the vehicle down. Fundamentally as always it comes down to shitty driving standards.

Okay so I haven't read the whole thread so this might have been answered but why do we still use side mirrors in cars. I would think that cameras would be a much better solution since they don't have the issue with perspective making things look further away. I would think that at least one company would have tried it by now unless there is some law requiring mirrors vs just being able to see.

Okay so I haven't read the whole thread so this might have been answered but why do we still use side mirrors in cars. I would think that cameras would be a much better solution since they don't have the issue with perspective making things look further away. I would think that at least one company would have tried it by now unless there is some law requiring mirrors vs just being able to see.

Cost would be a major factor if there aren't any regulations in that area. Mirrors are a lot cheaper than cameras, necessary screens, and required electronics/wiring. Mirrors also will still work if there are electrical issues.

Okay so I haven't read the whole thread so this might have been answered but why do we still use side mirrors in cars. I would think that cameras would be a much better solution since they don't have the issue with perspective making things look further away. I would think that at least one company would have tried it by now unless there is some law requiring mirrors vs just being able to see.

Regulatory burden.At least according to EU motorised vehicle regulatory rules (European Community Whole Vehicle Type Approval), all vehicles need to be equiped with side mirrors of certain size (plus a few more features). Exceptions are possible, e.g. for tiny car series (less than 1000) or exceptional circumstances. The webpage of the European Commission is actually pretty decent: http://ec.europa.eu/enterprise/sectors/automotive/

I am pretty sure that similar regulatory requirements exist in the US.

Okay so I haven't read the whole thread so this might have been answered but why do we still use side mirrors in cars. I would think that cameras would be a much better solution since they don't have the issue with perspective making things look further away. I would think that at least one company would have tried it by now unless there is some law requiring mirrors vs just being able to see.

Regulatory burden.At least according to EU motorised vehicle regulatory rules (European Community Whole Vehicle Type Approval), all vehicles need to be equiped with side mirrors of certain size (plus a few more features). Exceptions are possible, e.g. for tiny car series (less than 1000) or exceptional circumstances. The webpage of the European Commission is actually pretty decent: http://ec.europa.eu/enterprise/sectors/automotive/

I am pretty sure that similar regulatory requirements exist in the US.

Okay so I haven't read the whole thread so this might have been answered but why do we still use side mirrors in cars. I would think that cameras would be a much better solution since they don't have the issue with perspective making things look further away. I would think that at least one company would have tried it by now unless there is some law requiring mirrors vs just being able to see.

Regulatory burden.At least according to EU motorised vehicle regulatory rules (European Community Whole Vehicle Type Approval), all vehicles need to be equiped with side mirrors of certain size (plus a few more features). Exceptions are possible, e.g. for tiny car series (less than 1000) or exceptional circumstances. The webpage of the European Commission is actually pretty decent: http://ec.europa.eu/enterprise/sectors/automotive/

I am pretty sure that similar regulatory requirements exist in the US.

What I don't understand is why it seems so difficult for manufacturers to fix the problems with ABS, because an automated solution that works correctly should be able to perform as well as a superbly trained driver and be consistent.

This. Many or most implementations leave something to be desired.

Much worse, however, are the stability-control systems mandated by law on 2012 and newer model year autos in the U.S. Unlike ABS where the goal of the driver and engineer are ostensibly the same, stability control purposely disobeys the driver in favor programmed over-rides.

I had an interesting conversation with a professional test and development driver who also instructs - I put him in my racecar, and he recommended afterwards I go talk to Bosch about their motorsport ABS solution. It seems roadgoing ABS systems are heavily hampered by the fact that most drivers can't drive - so stopping the car quickly is less important than not inducing yaw, as Joe Average can't deal with that. There's also the problem as per Mercedes that if the car stops too quickly on the road, the dopey idiot behind is probably going to run into you.

The motorsport version expects the driver to be able to handle the ABS inducing heavy yaw rates - it will stop the car for you, but you're in charge of making sure it's pointed the right way at the end of it. I'm going to dig into this, as this may give a competitive advantage - I gather each wheel speed is measured individually, with accelerometer support, steering angle sensors, even centre of gravity.

I had an interesting conversation with a professional test and development driver who also instructs - I put him in my racecar, and he recommended afterwards I go talk to Bosch about their motorsport ABS solution. It seems roadgoing ABS systems are heavily hampered by the fact that most drivers can't drive - so stopping the car quickly is less important than not inducing yaw, as Joe Average can't deal with that. There's also the problem as per Mercedes that if the car stops too quickly on the road, the dopey idiot behind is probably going to run into you.

The motorsport version expects the driver to be able to handle the ABS inducing heavy yaw rates - it will stop the car for you, but you're in charge of making sure it's pointed the right way at the end of it. I'm going to dig into this, as this may give a competitive advantage - I gather each wheel speed is measured individually, with accelerometer support, steering angle sensors, even centre of gravity.

For competition it gets a lot more complicated. For instance, trailing brake into a corner loads the outside tires such that they will have greater traction. But larger braking forces –and drag- at the outside tires is just what you don’t want. Maybe this is handled with the steering angle. But it’s rather different from just not quite locking the brakes for the shortest straight line stopping distance.

I’ve always found it to be disconcerting when the car is doing its own thing that differs from my control input. But I have to admit that on a slimy test surface I couldn’t match the computer’s stopping distance when it was turned off.

I had an interesting conversation with a professional test and development driver who also instructs - I put him in my racecar, and he recommended afterwards I go talk to Bosch about their motorsport ABS solution. It seems roadgoing ABS systems are heavily hampered by the fact that most drivers can't drive - so stopping the car quickly is less important than not inducing yaw, as Joe Average can't deal with that. There's also the problem as per Mercedes that if the car stops too quickly on the road, the dopey idiot behind is probably going to run into you.

LED taillights give a very slight latency advantage that could conceivably help. Probably more important ergonomically would be variable-braking indication, as with taillights that grow brighter and more insistent, and pulse, as braking force increases.

I was hoping that the electronic braking systems -- specifically the low-voltage system originally developed by Siemens VDO -- would remove the feedback problems of hydraulic ABS, and perhaps even allow room for tuning of the sort you mean. I'm not sure of the chances it could have decent pedal feel, but anyway we haven't seen any such systems ship yet.

Braking yaw is specifically countered by the stability control mandated on all U.S. road cars.

Quote:

I gather each wheel speed is measured individually, with accelerometer support, steering angle sensors, even centre of gravity.

Add three computer-controlled differentials to the wheel instrumentation and that's all you need for full torque vectoring.

Might be a wee off topic, but I've often noticed in my car that the radio station I like often runs into interference related to my proximity to other cars. From the times where I've picked up other audio in my car (music, talk radio) I've assumed that this is related to people's relay devices : taking their phone / Sirius / whatever and pushing it out to be received by their own radio antenna. When it happens I can usually figure out what car it is that's overriding me and avoid them.

I'm surprised that these relay transmitters are powerful enough to do that, and then they are allowed to use that spectrum, but ok. But today was a strange one. There was a BMW that squelched out my radio signal if I was < 60 feet away (so, comparatively long range) and yet there was no bleed over audio, just silence. As it turns out, the BMW parked right next to me in the lot. I asked the driver when I got out if he had some radio repeater thing and he said he did not.

Is there some other piece of radio thing on the BMW that would do that? Or more likely, he has something and just forgot it was on? Is there some other source of interference that I'm not thinking of? I'm out of ideas.

Might be a wee off topic, but I've often noticed in my car that the radio station I like often runs into interference related to my proximity to other cars. From the times where I've picked up other audio in my car (music, talk radio) I've assumed that this is related to people's relay devices : taking their phone / Sirius / whatever and pushing it out to be received by their own radio antenna. When it happens I can usually figure out what car it is that's overriding me and avoid them.

I'm surprised that these relay transmitters are powerful enough to do that, and then they are allowed to use that spectrum, but ok. But today was a strange one. There was a BMW that squelched out my radio signal if I was < 60 feet away (so, comparatively long range) and yet there was no bleed over audio, just silence. As it turns out, the BMW parked right next to me in the lot. I asked the driver when I got out if he had some radio repeater thing and he said he did not.

Is there some other piece of radio thing on the BMW that would do that? Or more likely, he has something and just forgot it was on? Is there some other source of interference that I'm not thinking of? I'm out of ideas.

The problem is probable in the front end of your radio. The BMW may have had an auto-response system that reacts to a distance and/or closing rate signal such as autobraking, though I don’t know where in the EMS such a signal would live.

Might be a wee off topic, but I've often noticed in my car that the radio station I like often runs into interference related to my proximity to other cars. From the times where I've picked up other audio in my car (music, talk radio) I've assumed that this is related to people's relay devices : taking their phone / Sirius / whatever and pushing it out to be received by their own radio antenna. When it happens I can usually figure out what car it is that's overriding me and avoid them.

I'm surprised that these relay transmitters are powerful enough to do that, and then they are allowed to use that spectrum, but ok. But today was a strange one. There was a BMW that squelched out my radio signal if I was < 60 feet away (so, comparatively long range) and yet there was no bleed over audio, just silence. As it turns out, the BMW parked right next to me in the lot. I asked the driver when I got out if he had some radio repeater thing and he said he did not.

Is there some other piece of radio thing on the BMW that would do that? Or more likely, he has something and just forgot it was on? Is there some other source of interference that I'm not thinking of? I'm out of ideas.

That is really weird, while one of those relay devices could do that if you were close enough, for those to work well for the actual user you need to be broadcasting on a fairly clean frequency in the first place, essentially if there is a station broadcasting in your area that is much more than unintelligible static then they don't work well at all. It sounds to me like there is something wrong with your radio, you should not be getting crosstalk on FM channels at all. What kind of car, or head unit if you have changed it from stock? The radar used in the BMW collision avoidance system is way beyond the frequency range of FM radio but if a capacitor has died in one of the tuners filters it could be letting energy bleed into the receiver drowning out the wanted signal. A dead filter could also allow crosstalk, but I would expect it to happen more often than just with cars using relay transmitters. Does it only really happen on this one station? Maybe that station is near a popular "dead zone" in your area.

If you were just losing the station when near other cars that would be perfectly normal depending on signal strength and broadcast frequency, cars are very large conductors that can do funny things to rf signals.

I doubt there's anything wrong with his radio. I've observed the exact same thing in both my and my wife's car (Subaru and Mini). I've always assumed it was a radio adapter that was broadcasting at above the legal power level.

Yeah, stock radio (on a Prius, fwiw), haven't had any issues (well, the CD player is borked, but whatever). Typically if I tune to a different station I can get reception. (88.1 MHz I think). I usually get fine reception on my commute - and when it does get overridden it's almost always because some other signal cuts in. The BMW was odd because I got nothing at all over the radio and the fella driving it claimed he had no radio signal equipment running.

"Lasers can be focused and split into multiple beams to give multiple ignition points, which means it can give a far better chance of ignition. This can really improve the performance of the engine when it is cold, as this is the time when around 80 per cent of the exhaust emissions are produced and the engine is at is least efficient. The laser also produces more stable combustion so you need to put less fuel into the cylinder."

In current engines spark plugs are positioned at the top or bottom of a cylinder and they can often fail to ignite fuel effectively if the petrol is not in the right position in the cylinder. In the new system the spark plug is replaced by a laser powered by the car battery which is sent along thin optical fibres into the engine's cylinders where lenses focus the beam into an intense pinprick of light. When fuel is injected into the engine, the laser is fired, producing enough heat to ignite the fuel and power the engine. The researchers claim that the laser, which will need to fire more than 50 times per second to produce 3000 RPM, will require less power than traditional spark plugs. Some of the laser can be reflected back from inside the cylinder to provide information for the car on the type of fuel being used and the level of ignition, allowing the car to adjust the quantities of air and fuel automatically to optimise the performance.

Note that current ion-sensing techniques already derive feedback from current sparkplugs and are more granular and reliable than traditional knock sensors.